Moon Illusion and Emmert's Law.

Area of Science:

• Visual Perception
• Psychophysics
• Astronomy

Background:

• Emmert's Law describes the relationship between the apparent size of an afterimage and the distance of the surface on which it is projected.
• The sky is perceived as a flattened dome, influencing visual cues for distance and size.
• The moon illusion, where the moon appears larger near the horizon, is a common example of size perception phenomena.

Purpose of the Study:

• To investigate how the perceived size of an afterimage is affected by its projection location on the sky.
• To determine if Emmert's Law can predict afterimage size variations in relation to the sky's apparent dome shape.
• To draw parallels between afterimage perception and the moon illusion.

Main Methods:

• Participants viewed a stimulus and then projected an afterimage onto different parts of the sky.
• The perceived size of the afterimage was systematically measured.
• The observed variations were analyzed in the context of Emmert's Law and the perceived geometry of the sky.

Main Results:

• The perceived size of the afterimage varied significantly depending on whether it was projected onto the zenith or the horizon.
• These variations were accurately predictable using Emmert's Law, considering the sky as a flattened dome.
• The results demonstrated a direct analogy between afterimage size perception and the moon illusion.

Conclusions:

• The perceived size of projected visual stimuli, like afterimages, is influenced by the perceived distance cues of the projection surface.
• Emmert's Law provides a robust framework for understanding these size-distance relationships in the context of the sky's apparent geometry.
• The study reinforces the connection between afterimage perception and established optical illusions such as the moon illusion.